<!-- function.php -->

// Magnific Popup - Inline Content Enabler
function inline_popup_enabler(){
?>
<script>
(function($){
    $(window).load(function() {
        $('.inline_popup').magnificPopup({
          type:'inline',
          midClick: true 
        });
    });
})(jQuery);
</script>
<?php
}
add_action('wp_footer', 'inline_popup_enabler');

<!-- In the Page -->

<!-- Button Code -->
<div class="popup-button">
	<a href="#" data-mfp-src="#popup_content" class="inline_popup ">
		<span class="link-title">Read More</span>
	</a>
</div>

<!-- POPUP Content -->
<div id="popup_content" class="white-popup mfp-hide popup-content">
	<div class="popup-inner">
		#########
	</div>
</div>